Mitochondrial dysfunction has been implicated as a cause of age-related disorders;however little is known regarding the role of mitochondria in vascular disease. We recently found that estrogen (E) has beneficial effects on cerebrovascular mitochondria that likely contribute to vasoprotection. Thus, our overall hypothesis is: Effects of E on mitochondrial function protect against cerebrovascular endothelial dysfunction with age. In this proposal, mechanisms and consequences of E modulation of cerebrovascular mitochondria will be determined both in vitro and in vivo. Cultured human brain endothelial cells will be used in the first two aims. HYPOTHESIS 1: E increases the efficiency of oxidative phosphorylation and decreases oxidative stress in cerebral endothelial mitochondria. Key indices of mitochondrial function, mitochondrial enzyme levels and activities, mitochondrial biogenesis, and production of reactive oxygen species (ROS) will be measured after E treatment in normal conditions and in culture models of ischemia. The involvement of E receptors (ERalpha and ERbeta) will be tested using selective siRNA knockdown, antagonists, agonists and selective ER modulators (SERMs). HYPOTHESIS 2: E regulates mitochondrial function via PGC-1 transcriptional coactivators. We will determine effects of E, and the role of ERs, on levels of mitochondria-related transcription factors, including the PGC-1 family. Specific involvement of PGC-1[unreadable] in mitochondrial effects of E will be tested using siRNA downregulation of PGC-1[unreadable]. ER-PGC-1[unreadable] interactions will be tested by immunoprecipitation. In aim 3, a transgenic mouse model (MnSOD) will be used to test HYPOTHESIS 3: In vivo E protects cerebrovascular mitochondria and decreases endothelial dysfunction with advancing age. Cerebral blood vessels will be isolated from intact, ovariectomized, and E-treated females of different ages to compare mitochondrial enzymes, ATP and ROS production, and damage to mitochondrial iron/sulphur- containing enzymes and mtDNA. Endothelial function will be assessed in pressurized segments of isolated middle cerebral arteries. This project will delineate novel ways in which estrogen and estrogen-related therapies modulate the cerebral vascular system. These studies may provide insight into the role of mitochondria in cerebrovascular dysfunction, a contributor to age-related disorders such as stroke and vascular dementia.